1. Field of the Invention
This invention relates to a novel alkaline cellulase, and, more particularly, to a novel alkaline cellulase having an optimum pH in an alkaline range. The invention also relates to a process for preparing such an alkaline cellulase.
2. Description of the Background
Cellulases are recognized as a group of complex enzymes catalyzing enzymatic reactions decomposing cellulose and analogous polysaccharides into glucose, cellobiose, or into cello-oligosaccharides. Depending on the function, the cellulases encompass enzymes such as C.sub.1 enzyme, C.sub.x enzyme, exo-.beta.-glucanase, endo-.beta.-glucanase, endo-.beta.-1,4-glucanase (EC 3.2.1.4) [carboxymethyl cellulase (CMC-ase) or C.sub.x cellulase], exo-.beta.-1,4-glucanase (EC 3.2.1.91) (C.sub.1 cellulase or cellobiohydrolase), .beta.-1,4-glucosidase (EC 3.2.1.21) (cellobiase or .beta.-glucosidase), and the like. Conventionally, studies on cellulase have been directed, for the most part, to the effective utilization of biomass resources. For this reason major supply source of cellulase has been fungi belonging to the genera such as Trichoderma, Aspergillus, Acremonium, Humichola, and the like. Cellulases derived from microorganisms, including fungis, however, are different depending on their type with respect to specific actions of component enzymes, as well as in terms of physicochemical characteristics. The exact details have yet to be elucidated.
In recent years, industry has been developing new applications of cellulases, including, for example, the use of cellulases as additives for laundry detergents. Most of the cellulases produced by microorganisms in the natural world, at least those produced by the above-mentioned microorganisms, are acidic cellulases which have an optimum pH range of 4-6. They are deactivated in an alkaline pH range. There are few alkaline cellulases which exhibit maximum activity and resistance in an alkaline pH range, a range which is required for laundry detergents.
The only known processes for producing alkaline cellulases which can be used in laundry detergents are a process for collecting cellulase A from a culture broth of an alkalophilic microorganism belonging to the genus Bacillus (Japanese Patent Laid-open No. 28515/1975), a process for producing alkaline cellulase 301-A through culturing of a microorganism belonging to the genus Cellulomonas (Japanese Patent Laid-open No. 224686/1983), a process for obtaining carboxymethyl cellulase through culturing of an alkalophilic strain, Bacillus No. 1139 [Horikoshi et al, J. Gen. Microbiol., 131, 3339 (1985)], and a process for producing alkaline cellulase using a microorganism belonging to Streptomyces (Japanese Patent Laid-open No. 19483/1986).
Development of an alkaline cellulase which has an optimum pH in an alkaline range and which can be used as an enzyme in laundry detergents has therefore been desired.
In view of this situation, the present inventors have undertaken extensive investigations in order to find alkaline cellulase-producing microorganisms and found that a microorganism belonging to the genus Bacillus, which the inventors discovered and collected from the soil at Hagagun, Tochigi-ken, Japan, could produce a novel alkaline cellulase which is effective as an additive for laundry detergent compositions. This finding has led to the completion of this invention.